CN113608216A

CN113608216A - Satellite-borne multi-band common-caliber SAR and target combined on-orbit detection system and method

Info

Publication number: CN113608216A
Application number: CN202110710563.XA
Authority: CN
Inventors: 夏正欢; 张涛; 赵志龙; 刘敦歌; 张瑶; 刘新; 杨钰茜; 石慧峰; 岳富占
Original assignee: Space Star Technology Co Ltd
Current assignee: Space Star Technology Co Ltd
Priority date: 2021-06-25
Filing date: 2021-06-25
Publication date: 2021-11-05
Anticipated expiration: 2041-06-25
Also published as: CN113608216B

Abstract

The invention provides a space-borne multi-band common aperture SAR and a target joint on-orbit detection system and method. The system includes a three-band common-aperture antenna and a radar electronics system; the three-band common-aperture antenna adopts different forms of radiating elements in the three bands, and adopts a three-dimensional space arrangement to maximize the use of the antenna aperture; the radar The electronics system includes a radar main control unit, three IF signal generators, three up-conversion RF modules, three RF receivers, three down-conversion RF modules, three IF sampling high-speed ADCs, a clock manager and An on-board data memory, each band has an independent transmit channel and receive channel. The invention has high probability of detection and recognition of the target of the surface warship and strong timeliness.

Description

Satellite-borne multi-band common-caliber SAR and target combined on-orbit detection system and method

Technical Field

The invention relates to the technical field of radars, and provides a satellite-borne multiband common-caliber SAR and target combined on-orbit detection system and method.

Background

The satellite-borne SAR has all-weather imaging observation capability all day long, and is particularly suitable for detecting marine ship targets in cloud and mist weather. Under the condition of low sea, the sea clutter energy received by the single-station satellite-borne SAR is low, the ship sea contrast is high, and the ship target detection performance is high. However, under the condition of medium and high sea, the sea clutter energy is large, the dihedral angle scattering formed by the ship and the sea surface is weak, the ship-sea contrast is reduced rapidly, and the target detection performance is deteriorated. In order to realize reliable detection of a ship target under a medium-high sea condition, a multi-dimensional SAR concept is provided, namely, the multi-polarization electromagnetic scattering characteristic, the multi-wave band electromagnetic scattering characteristic, the multi-angle electromagnetic scattering characteristic and the like of the target are synchronously obtained, and the target detection performance is improved through multi-dimensional information fusion processing.

The American national space and aviation administration (NASA) space shuttle simultaneously carries an X-band SAR and a C-band SAR to carry out a series of tests such as interference height measurement, target detection and the like, and obtains global DEM information, but the antennas of the two bands are separated antennas, and the calibers of the two antennas are larger. E-SAR and F-SAR of an airborne multi-band SAR system of a German space navigation bureau (DLR) also prove the advantages of multi-band joint detection and target classification, and five band antennas of the F-SAR are also separate antennas and are respectively placed at different positions of an airplane. The NASA and the Indian Space Research Organization (ISRO) plan to transmit the first two-band SAR satellite NISAR in 2021, which can work in L-band and S-band simultaneously, and the two bands share a reflector antenna with a bore of 12m, but different array antennas are used as a feed source to feed the reflector antenna. In order to simplify the structure of the antenna with multiple bands and reduce the total area of the antenna, various common-aperture antenna technologies have been proposed. An L/S/X three-band common-caliber antenna is designed in 2019 by a national emphasis laboratory of aerospace five-institute five-good three-institute heaven-earth integrated information technology, each band has two polarizations, the L/S/X three-band common-caliber antenna effectively reduces the area and the weight of the antenna, and L, S and X three-band electromagnetic scattering information of sea surfaces and ship targets is synchronously obtained. After the three-band SAR image fusion processing, the SCNR and the contour information of the ship target are further improved, and the ship target detection performance under the medium and high sea conditions is improved.

Disclosure of Invention

The technical problem solved by the invention is as follows: the system and the method overcome the defects of the prior art, provide a satellite-borne multiband common-caliber SAR and a target combined on-orbit detection system and method, and solve the problems that in the prior art, a multiband SAR antenna is heavy, the ship target detection and identification probability under complex sea conditions is not high, and the timeliness is poor.

The technical scheme of the invention is as follows: a satellite-borne three-band SAR system comprises a three-band common-caliber antenna and a radar electronics system;

the three-band common-caliber antenna adopts different forms of radiation units in three bands respectively, and adopts three-dimensional spatial arrangement to realize maximum utilization of the caliber of the antenna;

the radar electronics system comprises a radar main control unit, three intermediate frequency signal generators, three up-conversion radio frequency modules, three radio frequency receivers, three down-conversion radio frequency modules, three intermediate frequency sampling high-speed ADCs, a clock manager and an on-satellite data memory, wherein each wave band is provided with an independent transmitting channel and an independent receiving channel.

The three-band common-caliber antenna can synchronously receive and transmit signals of three bands of L band, S band and X band; three-band SAR pulse is transmitted in an intra-pulse synchronous mode, signals of L, S and X bands are transmitted in sequence in a pulse repetition period PRP, and near-simultaneous receiving of the signals of the three bands is realized

And on the secondary outer layer part of the three-band common-caliber antenna, an L/S dual-band common-caliber scheme is adopted, namely an X-band radiation unit is removed on the basis of the L/S/X three-band common-caliber scheme, and an X-band radiation unit is adopted on the lower layer.

The central frequency of the L-band antenna array element is increased by 127 MHz; the area of the X-band SAR antenna is 4.8m multiplied by 0.6m, the area of the S-band SAR antenna is 7.2m multiplied by 1.2m, and the area of the L-band SAR antenna is 12.0m multiplied by 1.8 m.

The three-band SAR antenna comprises 10 antenna sub-boards, and the area of each antenna sub-board is 1.2m multiplied by 1.8 m; in the middle part of the antenna, a three-band common-aperture scheme is adopted, and the common-aperture antenna sub-array comprises a 6X 6X-band array, a 2X 2S-band array and two L-band units; selecting a printed monopole antenna with a U-shaped tuning branch as a radiation unit in an L wave band, and adopting coaxial direct feed; in the S wave band, a microstrip dipole which is orthogonally arranged is selected as a radiation unit, and microstrip lines are adopted to be close to the coupling feed; and in the X wave band, selecting a square patch and adopting slot coupling feeding.

Based on the synchronous emission capability of the three wave bands, a phased array mode is adopted to respectively adjust the beam directions of the three wave bands; the wave beams of the three wave bands can simultaneously point to the same area to acquire multi-band electromagnetic scattering information of a scene, and can also respectively point to different areas to realize more flexible functions.

The working mode of the three-band common-caliber antenna is as follows:

transmitting a three-band SAR pulse in an intra-pulse synchronization mode;

flexibly distributing three beam detection ranges according to target conditions;

the echo signals of the three wave bands are independently sampled in the distance direction and the azimuth direction.

A satellite-borne multi-band common-caliber SAR and target combined on-orbit detection method comprises the following steps:

1) signal level three-band joint detection;

2) imaging and preprocessing a target;

3) and carrying out three-band fusion detection and extraction on the target.

The signal-level three-band joint detection in the step 1) specifically comprises signal preprocessing and signal fusion processing;

the signal preprocessing comprises the steps of carrying out digital domain down-conversion on intermediate frequency echo signals of three wave bands, compressing distance direction pulses and carrying out orientation direction incoherent accumulation;

the signal fusion processing comprises the steps of carrying out decision-making fusion detection and constant false alarm rate detection processing on the echo signals of the three wave bands to obtain rough position information of the target.

The imaging and preprocessing method of the target in the step 2) specifically comprises the following steps:

imaging the target rough position information and the nearby area, registering the three-band images, and interpolating;

only imaging the area near the rough position of the target, wherein the range is not more than the sum of the position precision and the maximum length of the ship;

and performing registration based on imaging geometric information and image correlation, and interpolating the common detection region of the three images to the same geographic grid.

The specific method for target three-band fusion detection and extraction in the step 3) comprises the following steps:

denoising by using a wavelet threshold value, and cutting an image;

respectively generating multi-level wavelet coefficients for the three-band image;

performing weighted combination optimization by taking the maximized signal-to-noise-and-noise ratio and the strong point resolution as target functions to obtain weighted values of wavelet coefficients of all orders of the three-band image and obtain a fused image;

and extracting a target image according to the fused image, and forming an on-orbit detection product together with the target position and the position precision.

Compared with the prior art, the invention has the following beneficial effects: the method can synchronously obtain L, S and X three-waveband electromagnetic scattering information of a sea surface ship target, quickly position the ship target through signal and joint detection, improve the signal-to-noise-ratio and contour information of the ship target after the positioning area imaging and three-waveband image fusion processing, and improve the detection performance of the ship target under complex sea conditions. Compared with the traditional non-common-caliber multiband antenna and a sea surface ship target detection SAR system, the invention solves the problem of heavy weight of the multiband SAR antenna in the prior art, has high probability of detecting and identifying the sea surface ship target and high timeliness, and can realize the real-time detection and identification of the sea surface ship information with low cost and high efficiency.

Drawings

Fig. 1 is a schematic composition diagram of an on-board three-band SAR system according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a three-band common-aperture antenna for synchronously transmitting and receiving signals according to an embodiment of the present invention;

fig. 3 is a schematic diagram of a common layout and size of a three-band common-aperture antenna according to an embodiment of the present invention;

fig. 4 is a schematic diagram of a three-band SAR operation mode provided by an embodiment of the present invention;

FIG. 5 is a schematic diagram of a three-band SAR signal transmitting and receiving timing sequence provided by an embodiment of the present invention;

FIG. 6 is a schematic diagram of a three-band data joint processing method on a satellite according to an embodiment of the present invention;

FIG. 7 is a schematic diagram of a three-band signal level preprocessing method according to an embodiment of the present invention;

fig. 8 is a schematic diagram of a target three-band fusion detection and extraction method according to an embodiment of the present invention.

Detailed Description

In order to explain the technical means of the present invention, the following description will be given by way of specific examples.

Referring to fig. 1, a composition of a satellite-borne three-band SAR system is shown, and mainly includes two parts, namely a three-band common-aperture antenna and a radar electronics system. The radar electronics system mainly comprises a radar main control unit, three intermediate frequency signal generators, three up-conversion radio frequency modules, three radio frequency receivers, three down-conversion radio frequency modules, three intermediate frequency sampling high-speed ADCs, a clock manager, an on-satellite data memory and the like, wherein each wave band is provided with an independent transmitting channel and an independent receiving channel. The main parameters of the satellite-borne three-band common-aperture SAR system are shown in table 1, and echo signals of three bands are independently sampled in the distance direction and the azimuth direction.

TABLE 1 Main parameters of spaceborne three-band SAR system

The satellite-borne three-band SAR adopts a common-aperture antenna technology, and can synchronously receive and transmit signals of three bands, namely an L band, an S band and an X band, as shown in fig. 2.

In order to reduce the area and the weight of the three-waveband antenna as much as possible, an L/S/X three-waveband common-caliber antenna technology is adopted. Since the frequency ratio of the L/S/X three bands is about f_L：f_S：f_X1: 3: 9, wherein the center frequency of the L-band antenna element needs to be increased by about 127 MHz. Considering the performance of imaging resolution, width, noise equivalent scattering coefficient, azimuth ambiguity, distance ambiguity and the like, the area of the X-band SAR antenna is set to be 4.8 mx 0.6m, the area of the S-band SAR antenna is set to be 7.2 mx 1.2m, and the area of the L-band SAR antenna is set to be 12.0 mx 1.8m, as shown in fig. 3. The three-band SAR antenna comprises 10 antenna sub-boards, and the area of each antenna sub-board is 1.2m multiplied by 1.8 m. In the middle part of the antenna, a novel three-band common-aperture scheme is adopted, and the common-aperture antenna sub-array comprises a 6X 6X-band array, a 2X 2S-band array and two L-band units. In the L wave band, a printed monopole antenna with a U-shaped tuning branch is selected as a radiation unit, and coaxial direct feed is adopted. In the S wave band, a microstrip dipole which is orthogonally arranged is selected as a radiation unit, and a microstrip line is adopted to be close to the coupling feed. And in the X wave band, selecting a square patch and adopting slot coupling feeding. The radiation units in different forms are respectively adopted in the three wave bands, the three wave bands are arranged in a three-dimensional space, the mutual coupling between the three wave bands is reduced by more than 20% compared with the traditional plane arrangement, and the maximum utilization of the aperture of the antenna is realized. The antenna units of the three wave bands have broadband dual-polarization working capacity, and the working performance of the common-aperture SAR antenna is further improved.

And removing the X-band radiation unit on the basis of an L/S dual-band common-caliber scheme, namely an L/S/X three-band common-caliber scheme, at the secondary outer layer part of the antenna. Because the frequency of the three wave bands is large and the mutual influence is small, the working performance of the L/S dual-wave-band common-caliber sub-array is not changed greatly compared with the three-wave-band common-caliber sub-array. The advantage of this scheme is that it can ensure the flexibility of antenna array and expansion, and the radiation characteristic of each sub-array remains unchanged.

In the outmost layer part of the antenna, an L-waveband printed monopole antenna which is orthogonally arranged is adopted as a dual-polarized radiation unit, the form of the L-waveband unit is consistent with that of other units with the same caliber, and the expansion is easy. The effect of this part of the antenna is to increase the low band gain so that the gains of the three bands are relatively close.

The embodiment further provides a three-band SAR operation mode, which is detailed as follows with reference to fig. 4:

three-band SAR pulses are transmitted in an intra-pulse synchronization mode, signals of L, S and X bands are transmitted in sequence in a Pulse Repetition Period (PRP), near-simultaneous receiving of the signals of the three bands can be achieved, consistency of a target scene is guaranteed, and the transmitting and receiving time sequence is as shown in figure 5;

the three wave beam detection ranges are flexibly distributed according to the target condition, the wave beams of the three wave bands can simultaneously point to the same area, and scene multiband electromagnetic scattering information is obtained; the beams of the three wave bands can also respectively point to different areas, the L wave band works in a scanning imaging mode with medium resolution, an interested target is quickly detected, and then the S wave band and the X wave band are guided to carry out high-resolution imaging on the interested target.

The embodiment also provides a satellite real-time signal level three-band joint detection method, which comprises signal preprocessing and signal fusion processing, and the flow is shown in fig. 6.

S01, signal preprocessing comprises the steps of carrying out digital domain down-conversion on intermediate frequency echo signals of three wave bands in an orbit, compressing the distance direction pulse of the echo signals, and carrying out azimuth direction incoherent accumulation, so that a target can reach a signal-to-noise-and-noise ratio capable of carrying out rough detection, meanwhile, the satellite processing calculated amount is remarkably reduced, and the rapid detection of a ship target area is realized. As shown in fig. 7, the signal-to-noise-and-noise ratio is raised from 8dB (dark line) before processing to 22dB (light line);

the signal fusion processing comprises the steps of carrying out decision-level fusion detection and Constant False Alarm Rate (CFAR) processing on the signals after the three wave bands are preprocessed, and obtaining rough position information of the target.

And S02, imaging the target rough position information and the nearby area, registering the three-band image, and interpolating. The method is characterized in that:

only the area near the rough position of the target is imaged, and the range is not larger than the sum of the position precision and the maximum length of the ship. The calculated amount of the extracted small-area three-band imaging is very low, and the large-range sea surface ship target can be subjected to on-orbit imaging;

S03, the SCNR of the target can be greatly improved by three-band SAR image fusion processing, particularly the sea clutter energy in the middle and high sea state can be greatly inhibited, the edge profile and the details of the target are enhanced, the reliable detection and identification of the target are facilitated, the method comprises the steps of denoising by utilizing wavelet threshold and image cutting, and is characterized in that:

and respectively generating multi-level wavelet coefficients for the three-band image. Referring to fig. 8, an example shows the case of wavelet coefficient decomposition of j level and j +1 level, where L, S, and X represent bands, and subscripts 1, 2, 3, and 4 represent four kinds of coefficients, respectively, including two-dimensional scale coefficients, horizontal direction decomposition coefficients, vertical direction decomposition coefficients, and diagonal direction decomposition coefficients. The size of the area of each block represents the number of coefficients per block.

Taking j-level vertical decomposition coefficient (lower left corner color block in the figure) as an example, the three-band fusion result is P₄(j) The upper and lower index tables of the coefficient omega correspond to the types and wave bands of four decomposition coefficients. And performing the same operation on the corresponding coefficients of all levels and various types of the three wave bands, wherein the coefficients of all levels, various types and various wave bands are undetermined.

The fused image is

IM＝IWT(P)

Wherein P is the combination of all levels and various kinds of fused images according to the position of figure 8, and IWT is inverse wavelet transform.

The maximized signal-to-noise-and-noise ratio is taken as an objective function to carry out weighted combination optimization,

obtaining weighted values of wavelet coefficients of all orders of the three-band image to obtain a fused image;

The prediction method in the embodiment provides an airborne three-band common-aperture SAR system concept aiming at the detection application of the ship target under the condition of medium and high sea, reduces the area and the weight of the antenna by adopting a three-band common-aperture antenna technology, and synchronously obtains L, S and X three-band electromagnetic scattering information of the ship target on the sea surface. A three-band SAR echo information joint processing method is researched. Compared with the traditional single-band radar, after the fusion processing of the three-band SAR images, the signal-to-noise ratio is improved by using the L-band image and the S-band image under the condition of keeping the resolution of the X-band image as much as possible, the signal-to-noise ratio and the contour information of the ship target detection are improved, and the ship target detection performance under the condition of medium and high sea is improved.

Although the present invention has been described with reference to the preferred embodiments, it is not intended to limit the present invention, and those skilled in the art can make modifications and variations of the present invention without departing from the spirit and scope of the present invention.

Claims

1. a space-borne three-band SAR system, is characterized in that: comprise three-band common aperture antenna and radar electronics system;

The three-band common-aperture antenna adopts different forms of radiation elements in the three bands, and adopts a three-dimensional spatial arrangement to maximize the use of the antenna aperture;

The radar electronics system includes a radar main control unit, three intermediate frequency signal generators, three up-conversion radio frequency modules, three radio frequency receivers, three down-conversion radio frequency modules, three intermediate frequency sampling high-speed ADCs, and a clock Manager and an on-board data memory, each band has an independent transmit channel and receive channel.

2. A kind of space-borne three-band SAR system as claimed in claim 1, it is characterized in that: described three-band common aperture antenna can synchronously send and receive signals of three bands of L-band, S-band and X-band; adopt intrapulse synchronization It transmits three-band SAR pulses in a single pulse repetition period (PRP), and transmits signals in three bands of L, S, and X in sequence, so as to achieve near-simultaneous reception of signals in the three bands.

3. a kind of space-borne three-band SAR system as claimed in claim 2 is characterized in that: in the sub-outer layer part of the three-band common-aperture antenna, adopt L/S dual-band common-aperture scheme, namely L/S/X three Based on the band common aperture scheme, the X-band radiation unit is removed, and the X-band radiation unit is used in the lower layer.

4. A spaceborne three-band SAR system as claimed in claim 2, characterized in that: the center frequency of the L-band antenna array element is increased by 127MHz; the X-band SAR antenna area is 4.8m×0.6m, and the S-band SAR antenna The area is 7.2m×1.2m, and the area of the L-band SAR antenna is 12.0m×1.8m.

5. A kind of spaceborne three-band SAR system as claimed in claim 4 is characterized in that: three-band SAR antenna contains 10 antenna sub-boards in total, and the area of each antenna sub-board is 1.2m×1.8m; In the middle part, a three-band common aperture scheme is adopted. The common aperture antenna sub-array includes a 6×6 X-band array, a 2×2 S-band array, and two L-band units; in the L-band, a U-shaped tuning is selected. The printed monopole antenna of the branch is used as the radiating element, and the coaxial direct feeding is used; in the S-band, the orthogonally placed microstrip dipole is selected as the radiating element, and the microstrip line is used for close coupling feeding; in the X-band, the square patch and slot-coupled feed.

6. A kind of spaceborne three-band SAR system as claimed in claim 2, it is characterized in that: based on the ability of three-band synchronous transmission, adopt phased array mode, adjust the beam direction of three bands respectively; The beams of the bands can be directed to the same area at the same time to obtain multi-band electromagnetic scattering information of the scene, and can also be directed to different areas respectively to achieve more flexible functions.

7. a kind of spaceborne three-band SAR system as claimed in claim 2 is characterized in that: the working mode of described three-band common aperture antenna is:

Three-band SAR pulses are transmitted by intra-pulse synchronization;

The three beam detection ranges are flexibly allocated according to the target situation;

The echo signals of the three bands are independently sampled in the range and azimuth directions.

8. A space-borne multi-band common aperture SAR and target joint on-orbit detection method, characterized in that the steps are as follows:

1) Three-band joint detection of signal level;

2) Imaging and preprocessing the target;

3) Perform three-band fusion detection and extraction on the target.

9. A kind of spaceborne multi-band common aperture SAR and target joint on-orbit detection method according to claim 8, it is characterized in that: in described step 1), signal level three-band joint detection specifically includes signal preprocessing and signal fusion processing;

The signal preprocessing includes down-conversion in the digital domain of the intermediate frequency echo signals of the three bands, pulse compression processing in the range direction, and incoherent accumulation in the azimuth direction;

The signal fusion processing includes decision-level fusion detection and constant false alarm rate detection processing on the echo signals of the three bands to obtain the rough position information of the target.

10. A kind of spaceborne multi-band common aperture SAR and target joint on-orbit detection method according to claim 8, is characterized in that: the imaging and preprocessing method of target in described step 2) specifically comprises:

Perform imaging processing on the rough location information of the target and nearby areas, three-band image registration, and interpolation;

Only the area near the rough position of the target is imaged, and the range is not greater than the sum of the position accuracy and the maximum length of the ship;

Registration is performed based on imaging geometric information and image correlation, and the common detection area of the three images is interpolated to the same geographic grid.

11. a kind of space-borne multi-band common aperture SAR and target joint on-orbit detection method according to claim 8, is characterized in that: the concrete method of target three-band fusion detection and extraction in described step 3) comprises:

Use wavelet threshold to denoise and cut pictures;

Generate multi-level wavelet coefficients for three-band images respectively;

Taking the maximum signal-to-noise ratio and strong point resolution as the objective function for weighted combination optimization, the weighted value of each order wavelet coefficient of the three-band image is obtained, and the fusion image is obtained;

According to the fused image, the target image is extracted, and the on-orbit detection product is formed together with the target position and position accuracy.